Index: clang-tidy/readability/CMakeLists.txt
===================================================================
--- clang-tidy/readability/CMakeLists.txt
+++ clang-tidy/readability/CMakeLists.txt
@@ -12,6 +12,7 @@
   InconsistentDeclarationParameterNameCheck.cpp
   NamedParameterCheck.cpp
   NamespaceCommentCheck.cpp
+  NonConstParameterCheck.cpp
   ReadabilityTidyModule.cpp
   RedundantControlFlowCheck.cpp
   RedundantStringCStrCheck.cpp
Index: clang-tidy/readability/NonConstParameterCheck.h
===================================================================
--- clang-tidy/readability/NonConstParameterCheck.h
+++ clang-tidy/readability/NonConstParameterCheck.h
@@ -0,0 +1,64 @@
+//===--- NonConstParameterCheck.h - clang-tidy-------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_NON_CONST_PARAMETER_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_NON_CONST_PARAMETER_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace readability {
+
+/// Warn when a pointer function parameter can be const.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/readability-non-const-parameter.html
+class NonConstParameterCheck : public ClangTidyCheck {
+public:
+  NonConstParameterCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  void onEndOfTranslationUnit() override;
+
+private:
+  /// Parameter info.
+  struct ParmInfo {
+    /// Is function parameter referenced?
+    bool IsReferenced;
+
+    /// Can function parameter be const?
+    bool CanBeConst;
+  };
+
+  /// Track all nonconst integer/float parameters.
+  std::map<const ParmVarDecl *, ParmInfo> Parameters;
+
+  /// Add function parameter.
+  void addParm(const ParmVarDecl *Parm);
+
+  /// Set IsReferenced.
+  void setReferenced(const DeclRefExpr *Ref);
+
+  /// Set CanNotBeConst.
+  /// Visits sub expressions recursively. If a DeclRefExpr is found
+  /// and CanNotBeConst is true the Parameter is marked as not-const.
+  /// The CanNotBeConst is updated as sub expressions are visited.
+  void markCanNotBeConst(const Expr *E, bool CanNotBeConst);
+
+  /// Diagnose non const parameters.
+  void diagnoseNonConstParameters();
+};
+
+} // namespace readability
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_NON_CONST_PARAMETER_H
Index: clang-tidy/readability/NonConstParameterCheck.cpp
===================================================================
--- clang-tidy/readability/NonConstParameterCheck.cpp
+++ clang-tidy/readability/NonConstParameterCheck.cpp
@@ -0,0 +1,214 @@
+//===--- NonConstParameterCheck.cpp - clang-tidy---------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "NonConstParameterCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace readability {
+
+void NonConstParameterCheck::registerMatchers(MatchFinder *Finder) {
+  // Add parameters to Parameters.
+  Finder->addMatcher(parmVarDecl(unless(isInstantiated())).bind("Parm"), this);
+
+  // C++ constructor.
+  Finder->addMatcher(cxxConstructorDecl().bind("Ctor"), this);
+
+  // Track unused parameters, there is Wunused-parameter about unused
+  // parameters.
+  Finder->addMatcher(declRefExpr().bind("Ref"), this);
+
+  // Analyse parameter usage in function.
+  Finder->addMatcher(stmt(anyOf(unaryOperator(anyOf(hasOperatorName("++"),
+                                                    hasOperatorName("--"))),
+                                binaryOperator(), callExpr(), returnStmt(),
+                                cxxConstructExpr()))
+                         .bind("Mark"),
+                     this);
+  Finder->addMatcher(varDecl(hasInitializer(anything())).bind("Mark"), this);
+}
+
+void NonConstParameterCheck::check(const MatchFinder::MatchResult &Result) {
+  if (const auto *Parm = Result.Nodes.getNodeAs<ParmVarDecl>("Parm")) {
+    if (const DeclContext *D = Parm->getParentFunctionOrMethod()) {
+      if (const auto *M = dyn_cast<CXXMethodDecl>(D)) {
+        if (M->isVirtual() || M->size_overridden_methods() != 0)
+          return;
+      }
+    }
+    addParm(Parm);
+  } else if (const auto *Ctor =
+                 Result.Nodes.getNodeAs<CXXConstructorDecl>("Ctor")) {
+    for (const auto *Parm : Ctor->parameters())
+      addParm(Parm);
+    for (const auto *Init : Ctor->inits())
+      markCanNotBeConst(Init->getInit(), true);
+  } else if (const auto *Ref = Result.Nodes.getNodeAs<DeclRefExpr>("Ref")) {
+    setReferenced(Ref);
+  } else if (const auto *S = Result.Nodes.getNodeAs<Stmt>("Mark")) {
+    if (const auto *B = dyn_cast<BinaryOperator>(S)) {
+      if (B->isAssignmentOp())
+        markCanNotBeConst(B, false);
+    } else if (const auto *CE = dyn_cast<CallExpr>(S)) {
+      // Typically, if a parameter is const then it is fine to make the data
+      // const. But sometimes the data is written even though the parameter
+      // is const. Mark all data passed by address to the function.
+      for (const auto *Arg : CE->arguments()) {
+        markCanNotBeConst(Arg->IgnoreParenCasts(), true);
+      }
+
+      // Data passed by nonconst reference should not be made const.
+      if (const FunctionDecl *FD = CE->getDirectCallee()) {
+        unsigned ArgNr = 0U;
+        for (const auto *Par : FD->parameters()) {
+          if (ArgNr >= CE->getNumArgs())
+            break;
+          const Expr *Arg = CE->getArg(ArgNr++);
+          // Is this a non constant reference parameter?
+          const Type *ParType = Par->getType().getTypePtr();
+          if (!ParType->isReferenceType() || Par->getType().isConstQualified())
+            continue;
+          markCanNotBeConst(Arg->IgnoreParenCasts(), false);
+        }
+      }
+    } else if (const auto *CE = dyn_cast<CXXConstructExpr>(S)) {
+      for (const auto *Arg : CE->arguments()) {
+        markCanNotBeConst(Arg->IgnoreParenCasts(), true);
+      }
+    } else if (const auto *R = dyn_cast<ReturnStmt>(S)) {
+      markCanNotBeConst(R->getRetValue(), true);
+    } else if (const auto *U = dyn_cast<UnaryOperator>(S)) {
+      markCanNotBeConst(U, true);
+    }
+  } else if (const auto *VD = Result.Nodes.getNodeAs<VarDecl>("Mark")) {
+    const QualType T = VD->getType();
+    if ((T->isPointerType() && !T->getPointeeType().isConstQualified()) ||
+        T->isArrayType())
+      markCanNotBeConst(VD->getInit(), true);
+  }
+}
+
+void NonConstParameterCheck::addParm(const ParmVarDecl *Parm) {
+  // Only add nonconst integer/float pointer parameters.
+  const QualType T = Parm->getType();
+  if (!T->isPointerType() || T->getPointeeType().isConstQualified() ||
+      !(T->getPointeeType()->isIntegerType() ||
+        T->getPointeeType()->isFloatingType()))
+    return;
+
+  if (Parameters.find(Parm) != Parameters.end())
+    return;
+
+  ParmInfo PI;
+  PI.IsReferenced = false;
+  PI.CanBeConst = true;
+  Parameters[Parm] = PI;
+}
+
+void NonConstParameterCheck::setReferenced(const DeclRefExpr *Ref) {
+  auto It = Parameters.find(dyn_cast<ParmVarDecl>(Ref->getDecl()));
+  if (It != Parameters.end())
+    It->second.IsReferenced = true;
+}
+
+void NonConstParameterCheck::onEndOfTranslationUnit() {
+  diagnoseNonConstParameters();
+}
+
+void NonConstParameterCheck::diagnoseNonConstParameters() {
+  for (const auto &It : Parameters) {
+    const ParmVarDecl *Par = It.first;
+    const ParmInfo &ParamInfo = It.second;
+
+    // Unused parameter => there are other warnings about this.
+    if (!ParamInfo.IsReferenced)
+      continue;
+
+    // Parameter can't be const.
+    if (!ParamInfo.CanBeConst)
+      continue;
+
+    diag(Par->getLocation(), "pointer parameter '%0' can be pointer to const")
+        << Par->getName()
+        << FixItHint::CreateInsertion(Par->getLocStart(), "const ");
+  }
+}
+
+void NonConstParameterCheck::markCanNotBeConst(const Expr *E,
+                                               bool CanNotBeConst) {
+  if (!E)
+    return;
+
+  if (const auto *Cast = dyn_cast<ImplicitCastExpr>(E)) {
+    // If expression is const then ignore usage.
+    const QualType T = Cast->getType();
+    if (T->isPointerType() && T->getPointeeType().isConstQualified())
+      return;
+  }
+
+  E = E->IgnoreParenCasts();
+
+  if (const auto *B = dyn_cast<BinaryOperator>(E)) {
+    if (B->isAdditiveOp()) {
+      // p + 2
+      markCanNotBeConst(B->getLHS(), CanNotBeConst);
+      markCanNotBeConst(B->getRHS(), CanNotBeConst);
+    } else if (B->isAssignmentOp()) {
+      markCanNotBeConst(B->getLHS(), false);
+
+      // If LHS is not const then RHS can't be const.
+      const QualType T = B->getLHS()->getType();
+      if (T->isPointerType() && !T->getPointeeType().isConstQualified())
+        markCanNotBeConst(B->getRHS(), true);
+    }
+  } else if (const auto *C = dyn_cast<ConditionalOperator>(E)) {
+    markCanNotBeConst(C->getTrueExpr(), CanNotBeConst);
+    markCanNotBeConst(C->getFalseExpr(), CanNotBeConst);
+  } else if (const auto *U = dyn_cast<UnaryOperator>(E)) {
+    if (U->getOpcode() == UO_PreInc || U->getOpcode() == UO_PreDec ||
+        U->getOpcode() == UO_PostInc || U->getOpcode() == UO_PostDec) {
+      if (const auto *SubU =
+              dyn_cast<UnaryOperator>(U->getSubExpr()->IgnoreParenCasts()))
+        markCanNotBeConst(SubU->getSubExpr(), true);
+      markCanNotBeConst(U->getSubExpr(), CanNotBeConst);
+    } else if (U->getOpcode() == UO_Deref) {
+      if (!CanNotBeConst)
+        markCanNotBeConst(U->getSubExpr(), true);
+    } else {
+      markCanNotBeConst(U->getSubExpr(), CanNotBeConst);
+    }
+  } else if (const auto *A = dyn_cast<ArraySubscriptExpr>(E)) {
+    markCanNotBeConst(A->getBase(), true);
+  } else if (const auto *CLE = dyn_cast<CompoundLiteralExpr>(E)) {
+    markCanNotBeConst(CLE->getInitializer(), true);
+  } else if (const auto *Constr = dyn_cast<CXXConstructExpr>(E)) {
+    for (const auto *Arg : Constr->arguments()) {
+      if (const auto *M = dyn_cast<MaterializeTemporaryExpr>(Arg))
+        markCanNotBeConst(cast<Expr>(M->getTemporary()), CanNotBeConst);
+    }
+  } else if (const auto *ILE = dyn_cast<InitListExpr>(E)) {
+    for (unsigned I = 0U; I < ILE->getNumInits(); ++I)
+      markCanNotBeConst(ILE->getInit(I), true);
+  } else if (CanNotBeConst) {
+    // Referencing parameter.
+    if (const auto *D = dyn_cast<DeclRefExpr>(E)) {
+      auto It = Parameters.find(dyn_cast<ParmVarDecl>(D->getDecl()));
+      if (It != Parameters.end())
+        It->second.CanBeConst = false;
+    }
+  }
+}
+
+} // namespace readability
+} // namespace tidy
+} // namespace clang
Index: clang-tidy/readability/ReadabilityTidyModule.cpp
===================================================================
--- clang-tidy/readability/ReadabilityTidyModule.cpp
+++ clang-tidy/readability/ReadabilityTidyModule.cpp
@@ -20,6 +20,7 @@
 #include "ImplicitBoolCastCheck.h"
 #include "InconsistentDeclarationParameterNameCheck.h"
 #include "NamedParameterCheck.h"
+#include "NonConstParameterCheck.h"
 #include "RedundantControlFlowCheck.h"
 #include "RedundantSmartptrGetCheck.h"
 #include "RedundantStringCStrCheck.h"
@@ -57,6 +58,8 @@
         "readability-static-definition-in-anonymous-namespace");
     CheckFactories.registerCheck<readability::NamedParameterCheck>(
         "readability-named-parameter");
+    CheckFactories.registerCheck<NonConstParameterCheck>(
+        "readability-non-const-parameter");
     CheckFactories.registerCheck<RedundantControlFlowCheck>(
         "readability-redundant-control-flow");
     CheckFactories.registerCheck<RedundantSmartptrGetCheck>(
Index: docs/ReleaseNotes.rst
===================================================================
--- docs/ReleaseNotes.rst
+++ docs/ReleaseNotes.rst
@@ -85,6 +85,12 @@
   Warns about the performance overhead arising from concatenating strings using
   the ``operator+``, instead of ``operator+=``.
 
+- New `readability-non-const-parameter
+  <http://clang.llvm.org/extra/clang-tidy/checks/readability-non-const-parameter.html>`_ check
+
+  Flags function parameters of a pointer type that could be changed to point to
+  a constant type instead.
+
 Improvements to include-fixer
 -----------------------------
 
Index: docs/clang-tidy/checks/list.rst
===================================================================
--- docs/clang-tidy/checks/list.rst
+++ docs/clang-tidy/checks/list.rst
@@ -128,6 +128,7 @@
    readability-implicit-bool-cast
    readability-inconsistent-declaration-parameter-name
    readability-named-parameter
+   readability-non-const-parameter
    readability-redundant-control-flow
    readability-redundant-smartptr-get
    readability-redundant-string-cstr
Index: docs/clang-tidy/checks/readability-non-const-parameter.rst
===================================================================
--- docs/clang-tidy/checks/readability-non-const-parameter.rst
+++ docs/clang-tidy/checks/readability-non-const-parameter.rst
@@ -0,0 +1,48 @@
+.. title:: clang-tidy - readability-non-const-parameter
+
+readability-non-const-parameter
+===============================
+
+The check finds function parameters of a pointer type that could be changed to
+point to a constant type instead.
+
+When const is used properly, many mistakes can be avoided. Advantages when using
+const properly:
+ * prevent unintentional modification of data
+ * get additional warnings such as using uninitialized data
+ * make it easier for developers to see possible side effects
+
+This check is not strict about constness, it only warns when the constness will
+make the function interface safer.
+
+.. code:: c++
+
+  // warning here; the declaration "const char *p" would make the function
+  // interface safer.
+  char f1(char *p)
+  {
+    return *p;
+  }
+
+  // no warning; the declaration could be more const "const int * const p" but
+  // that does not make the function interface safer.
+  int f2(const int *p)
+  {
+    return *p;
+  }
+
+  // no warning; making x const does not make the function interface safer
+  int f3(int x)
+  {
+    return x;
+  }
+
+  // no warning; Technically, *p can be const ("const struct S *p"). But making
+  // *p const could be misleading. People might think that it's safe to pass
+  // const data to this function.
+  struct S { int *a; int *b; };
+  int f3(struct S *p)
+  {
+    *(p->a) = 0;
+  }
+
Index: test/clang-tidy/readability-non-const-parameter.cpp
===================================================================
--- test/clang-tidy/readability-non-const-parameter.cpp
+++ test/clang-tidy/readability-non-const-parameter.cpp
@@ -0,0 +1,279 @@
+// RUN: %check_clang_tidy %s readability-non-const-parameter %t
+
+// Currently the checker only warns about pointer arguments.
+//
+// It can be defined both that the data is const and that the pointer is const,
+// the checker only checks if the data can be const-specified.
+//
+// It does not warn about pointers to records or function pointers.
+
+// Some external function where first argument is nonconst and second is const.
+char *strcpy1(char *dest, const char *src);
+unsigned my_strcpy(char *buf, const char *s);
+unsigned my_strlen(const char *buf);
+
+// CHECK-MESSAGES: :[[@LINE+1]]:29: warning: pointer parameter 'last' can be pointer to const [readability-non-const-parameter]
+void warn1(int *first, int *last) {
+  // CHECK-FIXES: {{^}}void warn1(int *first, const int *last) {{{$}}
+  *first = 0;
+  if (first < last) {
+  } // <- last can be const
+}
+
+// TODO: warning should be written here
+void warn2(char *p) {
+  char buf[10];
+  strcpy1(buf, p);
+}
+
+// CHECK-MESSAGES: :[[@LINE+1]]:19: warning: pointer parameter 'p' can be
+void assign1(int *p) {
+  // CHECK-FIXES: {{^}}void assign1(const int *p) {{{$}}
+  const int *q;
+  q = p;
+}
+
+// CHECK-MESSAGES: :[[@LINE+1]]:19: warning: pointer parameter 'p' can be
+void assign2(int *p) {
+  // CHECK-FIXES: {{^}}void assign2(const int *p) {{{$}}
+  const int *q;
+  q = p + 1;
+}
+
+void assign3(int *p) {
+  *p = 0;
+}
+
+void assign4(int *p) {
+  *p += 2;
+}
+
+void assign5(char *p) {
+  p[0] = 0;
+}
+
+void assign6(int *p) {
+  int *q;
+  q = p++;
+}
+
+void assign7(char *p) {
+  char *a, *b;
+  a = b = p;
+}
+
+void assign8(char *a, char *b) {
+  char *x;
+  x = (a ? a : b);
+}
+
+void assign9(unsigned char *str, const unsigned int i) {
+  unsigned char *p;
+  for (p = str + i; *p;) {
+  }
+}
+
+void assign10(int *buf) {
+  int i, *p;
+  for (i = 0, p = buf; i < 10; i++, p++) {
+    *p = 1;
+  }
+}
+
+// CHECK-MESSAGES: :[[@LINE+1]]:17: warning: pointer parameter 'p' can be
+void init1(int *p) {
+  // CHECK-FIXES: {{^}}void init1(const int *p) {{{$}}
+  const int *q = p;
+}
+
+// CHECK-MESSAGES: :[[@LINE+1]]:17: warning: pointer parameter 'p' can be
+void init2(int *p) {
+  // CHECK-FIXES: {{^}}void init2(const int *p) {{{$}}
+  const int *q = p + 1;
+}
+
+void init3(int *p) {
+  int *q = p;
+}
+
+void init4(float *p) {
+  int *q = (int *)p;
+}
+
+void init5(int *p) {
+  int *i = p ? p : 0;
+}
+
+void init6(int *p) {
+  int *a[] = {p, p, 0};
+}
+
+void init7(int *p, int x) {
+  for (int *q = p + x - 1; 0; q++)
+    ;
+}
+
+// CHECK-MESSAGES: :[[@LINE+1]]:18: warning: pointer parameter 'p' can be
+int return1(int *p) {
+  // CHECK-FIXES: {{^}}int return1(const int *p) {{{$}}
+  return *p;
+}
+
+// CHECK-MESSAGES: :[[@LINE+1]]:25: warning: pointer parameter 'p' can be
+const int *return2(int *p) {
+  // CHECK-FIXES: {{^}}const int *return2(const int *p) {{{$}}
+  return p;
+}
+
+// CHECK-MESSAGES: :[[@LINE+1]]:25: warning: pointer parameter 'p' can be
+const int *return3(int *p) {
+  // CHECK-FIXES: {{^}}const int *return3(const int *p) {{{$}}
+  return p + 1;
+}
+
+// CHECK-MESSAGES: :[[@LINE+1]]:27: warning: pointer parameter 'p' can be
+const char *return4(char *p) {
+  // CHECK-FIXES: {{^}}const char *return4(const char *p) {{{$}}
+  return p ? p : "";
+}
+
+char *return5(char *s) {
+  return s;
+}
+
+char *return6(char *s) {
+  return s + 1;
+}
+
+char *return7(char *a, char *b) {
+  return a ? a : b;
+}
+
+char return8(int *p) {
+  return ++(*p);
+}
+
+void dontwarn1(int *p) {
+  ++(*p);
+}
+
+void dontwarn2(int *p) {
+  (*p)++;
+}
+
+int dontwarn3(_Atomic(int) * p) {
+  return *p;
+}
+
+void callFunction1(char *p) {
+  strcpy1(p, "abc");
+}
+
+void callFunction2(char *p) {
+  strcpy1(&p[0], "abc");
+}
+
+void callFunction3(char *p) {
+  strcpy1(p + 2, "abc");
+}
+
+char *callFunction4(char *p) {
+  return strcpy1(p, "abc");
+}
+
+unsigned callFunction5(char *buf) {
+  unsigned len = my_strlen(buf);
+  return len + my_strcpy(buf, "abc");
+}
+
+void f6(int **p);
+void callFunction6(int *p) { f6(&p); }
+
+typedef union { void *v; } t;
+void f7(t obj);
+void callFunction7(int *p) {
+  f7((t){p});
+}
+
+void f8(int &x);
+void callFunction8(int *p) {
+  f8(*p);
+}
+
+// Don't warn about nonconst function pointers that can be const.
+void functionpointer(double f(double), int x) {
+  f(x);
+}
+
+// TODO: This is a false positive.
+// CHECK-MESSAGES: :[[@LINE+1]]:27: warning: pointer parameter 'p' can be
+int functionpointer2(int *p) {
+  return *p;
+}
+void use_functionpointer2() {
+  int (*fp)(int *) = functionpointer2; // <- the parameter 'p' can't be const
+}
+
+// Don't warn about nonconst record pointers that can be const.
+struct XY {
+  int *x;
+  int *y;
+};
+void recordpointer(struct XY *xy) {
+  *(xy->x) = 0;
+}
+
+class C {
+public:
+  C(int *p) : p(p) {}
+
+private:
+  int *p;
+};
+
+class C2 {
+public:
+  // CHECK-MESSAGES: :[[@LINE+1]]:11: warning: pointer parameter 'p' can be
+  C2(int *p) : p(p) {}
+  // CHECK-FIXES: {{^}}  C2(const int *p) : p(p) {}{{$}}
+
+private:
+  const int *p;
+};
+
+void tempObject(int *p) {
+  C c(p);
+}
+
+// avoid fp for const pointer array
+void constPointerArray(const char *remapped[][2]) {
+  const char *name = remapped[0][0];
+}
+
+class Warn {
+public:
+  // CHECK-MESSAGES: :[[@LINE+1]]:21: warning: pointer parameter 'p' can be
+  void doStuff(int *p) {
+    // CHECK-FIXES: {{^}}  void doStuff(const int *p) {{{$}}
+    x = *p;
+  }
+
+private:
+  int x;
+};
+
+class Base {
+public:
+  // Ensure there is no false positive for this method. It is virtual.
+  virtual void doStuff(int *p) {
+    int x = *p;
+  }
+};
+
+class Derived : public Base {
+public:
+  // Ensure there is no false positive for this method. It overrides a method.
+  void doStuff(int *p) override {
+    int x = *p;
+  }
+};